Plastic anti-mould testing, also known as mould resistance or fungal resistance testing, evaluates the ability of polymeric materials to withstand colonization by mould fungi under warm and humid conditions. Performed by accredited third-party laboratories in accordance with international standards such as ISO 846, ASTM G21, and IEC 60068-2-10, these tests verify material durability, product safety, and regulatory compliance. This article explains the testing principles, sample requirements, evaluation criteria, and typical applications of anti-mould testing for plastics.
Technical Overview
Although the polymer backbone of most synthetic plastics is inherently resistant to microbial degradation, plastics frequently contain organic additives such as plasticizers, lubricants, stabilizers, processing aids, fillers, and cellulose-based reinforcements that can serve as nutrient sources for mould fungi. When plastic products are exposed to warm, humid environments, fungal colonization can cause surface staining, unpleasant odors, loss of optical clarity, embrittlement, reduction of mechanical strength, and deterioration of electrical insulation properties.
Plastic anti-mould testing simulates accelerated tropical or high-humidity service conditions by inoculating test specimens with a standardized suspension of fungal spores and incubating them on a nutrient-limited mineral salts agar. Because the medium itself contains no usable carbon source, any visible fungal growth must be supported by nutrients extracted from the test material. After a typical incubation period of 28 days, specimens are visually rated for growth intensity and, where required, assessed for changes in physical, optical, or electrical properties. The test is essential for validating antifungal formulations, qualifying materials for humid climates, and meeting buyer or regulatory requirements in sectors such as electrical equipment, automotive, packaging, and construction.
Testing Samples
Raw Materials and Compounds
Polymer resins, masterbatches, antifungal additives, and compounded pellets can be evaluated either as supplied or after being compression-molded or injection-molded into standardized plaques. Testing the compound itself allows material producers to characterize the intrinsic mould resistance of a formulation before it is converted into finished goods.
Finished Plastic Products and Components
Representative products include films, sheets, pipes and fittings, cable insulation and sheathing, gaskets and seals, appliance housings, automotive interior trim, footwear components, and medical device parts. Finished-product testing reflects the actual surface condition, processing history, and post-treatment of the item as delivered to the market.
Coated, Filled, and Modified Plastics
Painted or coated plastic parts, wood-plastic composites, flexible PVC, polyurethane foams, and plastics containing natural fibers or starch fillers are particularly susceptible to fungal attack and are frequently submitted for anti-mould verification. Samples treated with fungistatic or fungicidal agents are tested to confirm the efficacy of the protective treatment.
Typical specimen requirements include square pieces of approximately 50 mm × 50 mm (or the size specified by the applicable standard), with a thickness representative of the actual product, in a minimum of three to five replicate specimens plus positive and negative controls. Specimens should be cleaned of surface contamination and should not receive any cleaning or conditioning that would remove or deactivate the additive system being evaluated.
Testing Items
Depending on the standard selected and the purpose of the evaluation, plastic anti-mould testing may include the following assessment items:
- Visual fungal growth intensity rating on the specimen surface
- Determination of the fungistatic effect of the plastic material
- Assessment of the effect of soil microorganisms by soil-burial exposure
- Change in mass and dimensions after fungal exposure
- Change in mechanical properties such as tensile strength and elongation
- Change in optical properties such as color, gloss, and light transmission
- Change in electrical properties such as insulation resistance and dielectric strength
- Verification of the efficacy of antifungal additives and treatments
Testing Methods
ISO 846 – Plastics: Evaluation of the Action of Microorganisms
ISO 846 is the most widely applied international standard for evaluating the resistance of plastics to microorganisms. In the fungal growth test, specimens placed on mineral salts agar are inoculated with a mixed spore suspension of test fungi such as Aspergillus niger, Penicillium funiculosum, Paecilomyces variotii, Trichoderma viride, and Chaetomium globosum, then incubated for approximately four weeks under warm, high-humidity conditions. Growth intensity is rated on a scale from 0 to 5, where 0 indicates no growth visible even under magnification and 5 indicates growth covering more than 75 percent of the surface. The standard also defines methods for determining the fungistatic effect of a material, for assessing bacterial action, and for evaluating degradation caused by soil microorganisms.
ASTM G21 – Determining Resistance of Synthetic Polymeric Materials to Fungi
ASTM G21 is the predominant North American practice for fungal resistance testing of plastics. Specimens are placed on an agar medium containing only inorganic salts and inoculated with a mixture of five fungi, typically Aspergillus brasiliensis, Penicillium funiculosum, Chaetomium globosum, Trichoderma virens, and Aureobasidium pullulans. Incubation is conducted at 28 ± 1 °C with relative humidity of at least 85 percent for a minimum of 28 days. Results are reported on a visual rating scale from 0 to 4, where 0 represents no growth and 4 represents heavy growth covering 60 percent or more of the specimen surface.
IEC 60068-2-10 – Environmental Testing, Test J: Mould Growth
IEC 60068-2-10 addresses mould growth testing for electrotechnical products, including plastic enclosures, insulating components, and cable materials used in electrical and electronic equipment. Specimens are inoculated with a standardized fungal spore suspension and incubated under controlled cyclic temperature and humidity conditions for 28 days, with an 84-day extended severity available for critical applications. Evaluation combines visual growth rating with an assessment of functional effects such as changes in insulation resistance or corrosion of adjacent components, making this method particularly relevant for equipment intended for tropical or marine service environments.
GB/T 24128 – Plastics: Test Method for Resistance to Moulds
GB/T 24128 is the Chinese national standard for plastic anti-mould testing and is harmonized in principle with established international practices. Specimens on nutrient-limited agar are inoculated with a mixed fungal suspension, incubated for 28 days under specified temperature and humidity conditions, and rated for surface growth. This standard is commonly specified for products sold in the Chinese market, including PVC building materials, cables, and consumer goods.
JIS Z 2911 – Methods of Test for Fungus Resistance
JIS Z 2911 is the Japanese industrial standard covering fungus resistance testing for a wide range of materials, including plastics, coatings, and textiles. The method involves inoculating specimens with defined mould species and incubating them under humid conditions before assigning a growth rating. It is frequently requested for products supplied to Japanese OEMs and consumer markets.
Related Requirements Under UL Standards
Polymeric materials used in electrical equipment may also need to satisfy fungal resistance requirements referenced within UL material and equipment standards, which typically point to established practices such as ASTM G21 for demonstration of mould resistance. Accredited third-party laboratories can combine these evaluations with other weathering, flammability, and electrical safety assessments required for full material qualification.
Applications
Plastic anti-mould testing supports product development, quality control, and market access across many industries where plastics are exposed to humidity, condensation, or tropical climates:
- Wire and cable insulation and sheathing, particularly flexible PVC compounds
- Electrical and electronic equipment enclosures, connectors, and insulating parts
- Automotive interior components, seals, and trim exposed to humidity and condensation
- Packaging films and containers for food, cosmetics, and pharmaceuticals
- Building materials such as PVC flooring, wall coverings, profiles, and geomembranes
- Medical devices and hospital equipment housings requiring hygienic performance
- Marine, outdoor furniture, sporting goods, and footwear applications
- Wood-plastic composites, foams, adhesives, and coated plastic assemblies
FAQ
How long does a plastic anti-mould test take?
The standard incubation period is 28 days for most methods. Including spore preparation, sample conditioning, incubation, and report issuance, the total turnaround time at an accredited third-party laboratory is typically five to six weeks. Extended 84-day severities under IEC 60068-2-10 require correspondingly longer schedules.
What is the difference between ISO 846 and ASTM G21?
Both standards evaluate fungal resistance using mixed spore inoculation on a carbon-free mineral salts medium, but they differ in the fungal strains specified, incubation details, and rating scales. ISO 846 rates growth from 0 to 5 and additionally covers bacterial action and soil microorganism exposure, while ASTM G21 rates growth from 0 to 4 and focuses specifically on fungal resistance of synthetic polymeric materials. The choice depends on the target market and the specification invoked by the buyer or regulator.
What result is considered a pass?
In most specifications, a growth rating of 0 (no growth) or 1 (trace growth visible only under magnification per ISO 846, or less than 10 percent coverage per ASTM G21) is regarded as evidence of mould resistance. Materials showing no growth while the positive control exhibits vigorous growth are typically classified as fungistatic or resistant, subject to the acceptance criteria defined in the product standard or purchase agreement.
How are specimens evaluated beyond visual rating?
For engineering applications, visual rating can be supplemented by comparative measurements of mass, tensile and flexural properties, hardness, color and gloss, or electrical characteristics before and after fungal exposure. These quantitative results demonstrate whether fungal attack has caused functional degradation in addition to surface growth.
Can anti-mould testing verify antifungal additives?
Yes. Testing treated and untreated specimens in parallel demonstrates the efficacy of fungistatic or fungicidal additives. The fungistatic determination in ISO 846, which compares behavior on nutrient and nutrient-free media, further distinguishes between true material resistance and leachable biocidal action.
What sample information should be provided with a submission?
Applicants should specify the applicable standard and method, the intended test duration, the number of replicates, relevant material composition details including antifungal treatment, and any required post-exposure property measurements. Accredited third-party laboratories can assist in selecting the most suitable method and severity based on the product type, end-use environment, and destination market requirements.